With the advent of nanoelectronics, also called quantum effect electronics, device geometries can be downscaled to achieve significant increases in the functional density of integrated electronic systems. Improvements in functional density of up to an order of magnitude relative to conventional circuitry can be obtained through the use of the natural serpentine switching characteristic of quantum device. F. Capasso, S. Sen, F. Beltram, "Quantum-Effect Devices," High speed Semiconductor Devices. ed. by S. M. Sze, (John Wiley New York 1990) pp. 465-520. These devices display multiple on/off switching transitions as a function of their control inputs so that an entire logic function can be provided by a single switching component. These increases in functional density are particularly important for digital electronics, since there are limits to the scaleability of conventional transistors and wherein the need to increase the performance of integrated circuits is ever-pressing.
Additional increases in functional density can be obtained if arithmetic calculations can be performed in a higher logic radix than the traditional binary of radix-2 method. Conventional logic circuitry is based on 2-state or binary switching components. The pressure to reduce interconnection complexity and chip area provided early impetus to developing three-level (ternary) and n-level (n-ary) computing devices. Multivalued logic (MVL) circuits can also be used to compensate for faults within circuitry by using the extra levels to provide redundancy. Theoretically, average circuit wiring length and intricacy reduce with device radix. Gate count also tends to drop with increasing radix, since fewer devices are required to specify the state variables of the function. For example, ternary multipliers require fewer than 60% of the number of interconnections and 80% of the devices necessary in the equivalent binary configuration. Z. G. Vranesic and V. C. Hamacher, "Ternary Logic in Parallel Multipliers," Journal of Computation Vol. 15, No. 3, p. 2.54 (1972). Thus, multivalued technology has great potential for increasing circuit density and speed.
The lack of an adequate device technology has hampered the widespread development of MVL integrated circuits. To maintain noise immunity, it is essential that the transfer characteristic of MVL devices contain multiple plateaus of stable intermediate levels between power rails. Assuming the availability of circuit synthesis tools, the feasibility of the MVL approach depends critically upon the development of practical switching devices. Historical attempts to develop practical implementations of multivalued devices have not been successful. Early examples include the parametron, the Rutz transistor, and various ferrite loop devices. Ultimately, these approaches gave way to MVL circuits built up from binary devices that were arranged to exhibit a multivalued characteristic. But, conventional digital devices such as MOS transistors have a step-like switching characteristic that do not admit a natural multilevel operating mode. Multi-valued logic circuits use fewer logic gates and interconnections to perform the same arithmetic operations, thus saving circuit area and increasing the speed of calculations. Z. G. Vranesic and V. C. Hamacher, "Ternary Logic in Parallel Multipliers," Journal of Computation Vol. 15, No. 3, p. 254 (1972).
Therefore, the need has arisen for a quantum effect logic gate capable of performing complex logic functions within a single device. Furthermore, a need has arisen for such a quantum device that operates at room temperature and higher, and which can be electrically programmed to provide multiple logic operations in binary and multi-valued arithmetic circuits.